Load Flow Analysis of Multi-Converter Transmission Systems

This thesis discusses the development of a load flow methodology capable of solving for the load flow of power systems inclusive of multiple point-to-point HVDC links. The methodology is an extension of a previous algorithm developed by Sato and Arillaga. Recent pushes for renewable power and developments supporting HVDC transmission for short distances will facilitate the substitution of multiple HVDC links for existing transmission lines. The extended methodology is utilized as a load flow analysis tool and is applied to various power systems to determine the effects of multiple HVDC links on the convergence properties of the load flow methods (i.e. timing and number of iterations). It was found that the percentage of DC transmission in a system is a good indicator of which embedded AC load flow method should be utilized in the extended methodology. Specifically at a DC transmission percentage of 90% or higher, the Gauss Seidel method has speeds comparable to the Newton-Raphson method. Leveraging off this finding, an Enhanced Load Flow solver is developed, which optimizes for faster convergence with a second priority to reducing memory requirements. The Enhanced Load Flow solver is a robust methodology which is easily extended to include other AC load flow methods. This research also looked into the effects of substituting AC transmission lines with HVDC links on the speed of convergence for voltage stability studies. It was found that the substitution of HVDC links for lines connected to a heavily loaded bus for a stressed system yields a lower convergence time for the voltage stability study